Thanks. So it seems that this problem is somehow specific to poclbm. And it's the old version that was working before ?
I can confirm this. Also I have poclbm miners that are currently working, but once you stop them they will no longer work upon re-start.
I just checked other forum threads and noticed same problem reported by users from at least 3 or more pools, so it may be somehow caused by poclbm itself.
That's very strange because it was the best miner ever.
My logs show that those workers just stop submitting any shares, don't see any reason yet.